This invention relates to a device for applying an axial load to a member and in which the force applied by said device differs under differing operating conditions.
One example of apparatus in which such axial loading device is used is a variable ratio frictional drive gear of the kind comprising basically two axially spaced torus discs or rotors, one serving as an input and the other an output, between which there is a set of circumferentially spaced drive rollers in frictional rolling contact with part toroidal surfaces on the discs, each roller being rotatably mounted in a bearing structure which can tilt about an axis at right angles to the axis of rotation of each roller so as to vary distances from the gear axis at which the roller engages the two discs respectively, thus varying the drive ratio of the gear. The angle of tilt of the roller bearing structure as it controls the drive ratio of the gear is called the ratio angle. There is furthermore provided means which is normally fluid pressure operated, for loading the discs axially so that there is pressure between the toroidal surfaces and the surfaces of the rollers engaging them.
One way of changing the ratio angle is to provide means to apply a force to each of the roller bearing structures to move it generally tangentially with respect to the gear axis, and by allowing the rollers then to steer themselves towards a different ratio angle. The rollers are each mounted in their bearing structures in such a way that they are inclined at an angle to a plane perpendicular to the gear axis. This angle is called the caster angle. Gears of this general construction are referred to as gears with tangentially controlled roller bearing structures.
End loading, as the axial loading under fluid pressure is usually called, must be substantial, though when hydraulic pressure is not available it is still necessary for some force to be applied. Furthermore the higher the speed and the higher the load, being transmitted through the transmission system the higher the pressure must be in order to maintain frictional contact between the rotor toroidal and roller surfaces, in order, in turn, to maintain efficiency of load transmission. The frictional contact may be through the agency of lubricating fluid which in this type of apparatus is usually referred to as tractant fluid.
The input must rotate in the direction in which it tends to drag each roller against the control force which controls the tangential position of the rollers. The caster angle must be such that each roller tilt axis is inclined away from the input disc in the direction of movement of the disc. This criterion arises out of the fact that stable operation at any given ratio angle occurs when the axis of rotation of each roller passes through the gear axis. Unless the caster angle is as just described, tangential displacement of a roller (by virtue of an increase or decrease in the load on the gear or in controlling fluid pressure will result in the torus discs producing a steering force on the roller which will tilt the roller in the direction opposite to that which is required to move the roller axis back to intersect the gear axis, so that the roller will be moved away from, instead of towards, its new stable position.
This invention is particularly though not exclusively concerned with gears in which the plane of each roller normal to the axis of rotation of the roller and passing through the points of contact of the roller with the two opposed torus discs, contains the axis about which the roller tilts, being tangential to the torus centre circle (i.e. the locus of the centre of the circle revolved to generate the torus) as distinct from gears in which the same plane for each roller is closer to the main axis of rotation of the gear.
The object of the invention is to provide a device for applying axial loading to a member in an effective manner in varying operating conditions.
According to the invention an axial loading device for applying an axial load to a member includes spring means acting between an abutment and the member, which is axially movable relative to said abutment, the spring means acting on one part of said member in a first axial position of said member and acting on a further part of said member when it is in a further axial position, the said one part of the member being spaced from the said further part of said member, such that different axial loading is applied to said member by said spring means when the member occupies said first and said further axial positions respectively.